Sharp PC-1500 : Bombing game

You're that pixel flying horizontally across the screen, and
you drop bombs (one at a time) over structures at the bottom of
the screen. Over time, you fly closer and closer to the ground,
until the final crash...

Hitting a 4-pixels structure gives you 4 points, a 3-pixels
structures gives you 3 points, and so on. When you hit a
structure, it becomes one pixel smaller.
If you manage to destroy all the 4-pixels structures, you get a
bonus when you sucessfully cross the screen at a height where you
should have crashed into one of them. Same for 3-pixels
buildings, but you probably won't go that far!

Start the program with DEF A or RUN.
The program then randomly creates the "city". SPACE drops a bomb. Next bomb can be dropped only after
the previous hits something.